If you are one of the 34 million or so Americans who claim descent from predominantly Irish roots, then March 17 probably holds special significance for you. Tradition-minded sons and daughters of Ireland hold it as a day to honor their homeland’s patron saint, a Briton named Padraig, or Patrick, who converted clans across the island to Christianity.

The less devout will tip a mug to the saint, thinking that his day is one to celebrate whoever it was who invented beer. For them, St. Patrick’s Day is one for green clothing, green-dyed hair, and green beer—and quite possibly a green complexion the next day. It’s a day for parades, for singing traditional songs, for eating colcannon and corned beef. One need not even be Irish to enjoy it, for an Irish American tradition of long standing is that no questions are asked: on St. Patrick’s Day, regardless of true ethnic origins, everyone is Irish.

It was not always this way. The first known St. Patrick’s Day celebration in New York was held in 1762, when Irish soldiers enrolled in the ranks of the British army marched down Broadway in a display of ethnic pride. Some of them stayed when their enlistments expired, and New York, then as now, became a center of Irish immigration to America. In later decades, the New York Irish would organize parades on March 17, a different one for each neighborhood, church, and fraternal order. They would eventually come together in one parade in the 1850s, and New York has held a big St. Patrick’s Day parade ever since.

Apart from that city and Boston, Savannah, and a few other East Coast centers of Irish settlement, though, March 17 was just another day. Elsewhere in the United States, that began to change later in the nineteenth century, when Irish immigrants streamed across the ocean to escape poverty, famine, and violence. They brought their prejudices and differences with them. A great gulf persisted between Irish Catholics and Irish Protestants, who viewed each other with mutual suspicion and fear, even though they lived across the road from one another, ate the same food, drank the same water—and, yes, beer. The Catholic newcomers celebrated March 17, and, led by groups such as the Ancient Order of Hibernians, turned the day into an expression of Catholic, anti-British expression, especially in Chicago.

Protestants, for their part, tended to ignore the day, preferring to celebrate July 12, in commemoration of the Battle of the Boyne, when forces loyal to the Protestant Dutch king of England defeated those of the Catholic Scottish claimant to the throne. They wore orange, in honor of the Dutch House of Orange, while the Catholics wore green, the color of the shamrock, even though to do so was to tempt fate—for, in Irish folklore, green is the favorite color of the fairies, who, out of jealousy, have a tendency to kidnap humans who wear too much of it.

As back home in Ireland, those orange and green parades had a bad habit of turning into fights, often fueled by too much of the drink. Things got so bad in Chicago that in 1870 the Catholic leadership excommunicated the most vocal of the anti-British, anti-Protestant Fenians, who, for a few years, organized their own St. Patrick’s Day parade and kept on scuffling. The Ancient Order of the Hibernians, loyal to the church leadership, attempted to turn the celebration into a religious one in which alcohol was banned outright, an idea that took no time at all to crash to the ground. Even so, the ethnic tensions began to relax as the years went by, while Protestant clergy, too, encouraged their flocks to calm down and forget the old rivalries in the New World.

The new mood suited the call for peace, understanding, and ethnic harmony that St. Patrick himself carried. Legend has it that Patrick came to Ireland from what is now England in the fifth century. His introduction to the country was not of Patrick’s making, for he was kidnapped as a teenager by roving brigands and brought to Antrim, in the north of Ireland. There he lived in slavery for six years before escaping. He took the long way around, a stowaway on a ship to Gaul, or France. In time he returned to his parents’ home. Not long after his homecoming, though, he had a vision that he would return to Ireland and lead the people there to Christianity. Patrick entered a seminary, studied the Bible, and returned fourteen years after he fled, and for the next thirty years Patrick built churches and sanctuaries, converted thousands, and, according to legend, expelled all the serpents from Ireland.

America still has its snakes, of course. And whereas in Ireland St. Patrick’s Day is generally observed as a day of peace across religious lines, here, like Christmas, the religious significance of the holiday has taken second place to secular interests. Irish Catholics and Protestants no longer battle in the streets of New York, Boston, and Chicago, and even if they observe a few differences (Catholics drink Jameson’s whiskey, for example, and Protestants Bushmill’s, except when they do it the other way around, just to confuse things nicely), the day is likely not to have sectarian meaning, its religious dimension involving only the dim memory of that snake-ousting saint of old, whose biographical details few remember.

What the day has become, instead, is a day to express Irish American identity. If that expression is sometimes trivial, all “kiss me, I’m Irish” buttons and green shamrock pins, it is nevertheless meaningful to millions and millions of Americans. Happily, times have changed on both sides of the water, with less fighting and less to fight about. That in itself is a fitting memory to Patrick, that great messenger of peace.